brand: new e-mark (Euler's e + ἐφάπαξ), fix README hero positioning (#339)

**Fixes the "weird" hero + gives you a social image.**

- The old hero was a 1587×2245 **portrait** shown at 460px — it read as
an oversized accidental drop-in. Replaced with a small centred
**e-mark** icon (150px).
- New mark is *e-like*: a glowing italic **mathematical e** (Euler's
*e*) in brand amber inside the concentric region rings.\n- Reordered the
README header into valid AsciiDoc — **title/attributes first**, then
hero, tagline, badges (previously the badges and image sat *before* the
doctitle, which is what mangled the top of the page).\n\n**Assets**\n-
`brand/e-mark.png` — 512px square icon (README hero)\n-
`brand/social-preview.png` — 1280×640 card (*e* + ephapax + **ἐφάπαξ —
once for all**)\n\n**Owner action:** upload `brand/social-preview.png`
at **Settings → General → Social preview** (no API for it). A copy is
also in your Downloads.\n\n_The old `brand/hero/social-profile.png` is
left in place; delete it if unused._\n\nDraft so you can eyeball the
render.\n\n🤖 Generated with [Claude
Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

README.adoc

@@ -1,11 +1,3 @@
-image:https://img.shields.io/badge/OpenSSF-Best_Practices-green?logo=opensourcesecurity[OpenSSF Best Practices,link="https://www.bestpractices.dev/en/projects/new?repo_url=https://github.com/hyperpolymath/ephapax"]
-image:https://img.shields.io/badge/License-MPL--2.0-blue.svg[License: MPL-2.0,link="https://www.mozilla.org/MPL/2.0/"]
-image:https://img.shields.io/badge/Philosophy-Palimpsest-indigo.svg[Palimpsest,link="https://github.com/hyperpolymath/palimpsest-license"]
-image:https://github.com/hyperpolymath/ephapax/actions/workflows/codeql.yml/badge.svg?branch=main[CodeQL,link="https://github.com/hyperpolymath/ephapax/actions/workflows/codeql.yml"]
-image:https://api.thegreenwebfoundation.org/greencheckimage/ephapax.org[Green Hosting,link="https://www.thegreenwebfoundation.org/green-web-check/?url=ephapax.org"]
-
-image::brand/hero/social-profile.png[ephapax,align="center",width=460]
-
 // SPDX-License-Identifier: CC-BY-SA-4.0
 // Owner: Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
 // SPDX-FileCopyrightText: 2025-2026 Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
@@ -17,8 +9,16 @@ image::brand/hero/social-profile.png[ephapax,align="center",width=460]
 
 = Ephapax
 
+image::brand/e-mark.png[ephapax,align="center",width=150]
+
 _ἐφάπαξ — once for all._
 
+image:https://img.shields.io/badge/OpenSSF-Best_Practices-green?logo=opensourcesecurity[OpenSSF Best Practices,link="https://www.bestpractices.dev/en/projects/new?repo_url=https://github.com/hyperpolymath/ephapax"]
+image:https://img.shields.io/badge/License-MPL--2.0-blue.svg[License: MPL-2.0,link="https://www.mozilla.org/MPL/2.0/"]
+image:https://img.shields.io/badge/Philosophy-Palimpsest-indigo.svg[Palimpsest,link="https://github.com/hyperpolymath/palimpsest-license"]
+image:https://github.com/hyperpolymath/ephapax/actions/workflows/codeql.yml/badge.svg?branch=main[CodeQL,link="https://github.com/hyperpolymath/ephapax/actions/workflows/codeql.yml"]
+image:https://api.thegreenwebfoundation.org/greencheckimage/ephapax.org[Green Hosting,link="https://www.thegreenwebfoundation.org/green-web-check/?url=ephapax.org"]
+
 [IMPORTANT]
 .Not to be confused with AffineScript
 ====